Conventionally, a vehicle comprising a collision avoidance assist device has been known. The collision avoidance assist device decelerates the vehicle by an automatic brake, when an obstruction, with which a self-vehicle will collide with a high possibility, is detected by a sensor, such as radar. For instance, a crash cushion proposed in the Patent Document 1 (PTL1), calculates a predicted collision time until a self-vehicle and an obstruction collide, brings an automatic brake 1 into operation when this predicted collision time becomes less than an assist time, and brings an automatic brake 2 into operation when this predicted collision time becomes less than a reduction time shorter than the assist time. This automatic brake 1 is a brake for warning and assisting a collision avoidance operation by a driver, and the automatic brake 2 is a brake for reducing the damage at the time of a collision of a vehicle and an obstruction. Therefore, the automatic brake 1 brings a vehicle to stop with a smaller deceleration as compared with that of the automatic brake 2. In addition, in this specification, the magnitude of deceleration refers to the absolute value of deceleration.